There is no dipstick, there is a plug at the side of the transmission to check the level.
Tow it to a Ford dealership, it might be covered under their power train warranty, but don't temper with it - it could avoid the warranty.
...looks & runs good & has done more than expected for so many years & miles, until now.
The transmission has become completely inoperable, it will not at all go into any gear, forward or reverse. It...